Remember I told you that Grandpa Byron can remember pretty much every single day of his life? Now I think about it a bit more, it’s easily the most impressive thing he does.

Some of what he remembers are big things, like getting married – which everyone remembers – but some can be tiny, like having a particularly nice lunch, or what he wore that day.

So far, it makes for more than eighteen thousand bits of information that he can call up when he wants to remember, say, where he was on a particular day, or where he was living, or who was with him, or what he ate. None of it’s written down, of course, so there’s no way I can check whether he’s right, but I trust him.

A date might be mentioned on the radio, and he’ll close his eyes and say, “Ah, yes! March 12th 1977. That was the day me and your Grandma Julie walked along the beach and there was the most jolly terrific hailstorm, great big hailstones as big as peas,” and sometimes he can do added details like who else was there and what they were wearing, but not always.

Anyway, we are back at Grandpa Byron’s house, stiff from the moped ride, and I need to check something. We have hardly said a word on the way back, mainly because it’s virtually impossible to talk over the whining of the engine and the wind in our faces, and besides, there’s not much to say that doesn’t involve me saying sorry for having messed it all up.

“How are the old Memory Palaces, Grandpa Byron?” I ask with what I hope is a casual voice, but I wasn’t to know the reaction this would provoke. He goes very, very quiet and he scowls and I honestly don’t think I’ve seen Grandpa Byron scowl before.

“Requiring a little maintenance, I’d say.”

“OK. So what were you doing on, ooh … September 2nd, 1980?”

His eyes look up to the left for the longest time. “That was, erm … Like I say, they are requiring a little upkeeping.”

I am disappointed and can’t help showing it. “Oh come on – what about January 24th, 1996?”

Grandpa Byron snaps at me, “Don’t! I am not a performing flipping monkey.”

But I don’t give up. “You wrote the book, though! The Memory Palaces of the Sri—”

“I know what I did, and so do you, apparently. Everything about ‘me’. Except that it seems to be some other ‘me’,” and to emphasise what he’s saying, he makes quote marks in the air with his fingers. His voice is quite loud now. “I have never seen that book in years, I have never seen you for thirty years, and now you are expecting me to be someone else? Think about what you are asking, Al. I’m going to the shops. You stay here. I’m not wanting you to walk the streets. It’s not safe. And afterwards we need to work out what to do with you.”

What he means is it is not safe for him. I get it. A man cannot suddenly have a young boy live with him without people wanting to know why.

The front door slams as he leaves, and that now makes two rows I have had with Grandpa Byron both within about five days, or thirty years, or oh, I don’t know … take your pick. I’ve pretty much given up trying to work it out.

I hear Grandpa Byron’s scooter coughing down the street and I have to act fast.

The thing is this: I have come back to a world that has changed in a billion unknowable ways as a result of what I did. Mum doesn’t know me (other than meeting me once and thinking I’m ‘special’), Grandpa Byron’s just … well, he’s just not the same. I worked this out on the journey back from Blaydon when I remembered what Grandpa Byron (or who I am now beginning to think of as ‘the old Grandpa Byron’) told me:

“Don’t dream of a different life, Al. Love the one you’ve got.”

Does that mean I can’t try to change the one I’ve got? I have decided that it doesn’t. From my backpack in Pye’s bedroom, I take out the scratched and battered black box and the cables. The string of numbers and symbols that I so laboriously typed into Pye’s supercomputer is still on my key-ring memory stick. I’ll need to borrow Grandpa Byron’s laptop. I’ll need to find a zinc garden tub from somewhere.

I am going to use the time machine one last time.

And I mean it. One. Last. Time.

I am sick to death of time travel.